There are currently numerous sensors on the market for detecting the level in a container or on a stockpile. Sensors that detect the level using guided radar waves or radar waves that radiate into free space are particularly important.
These level measuring instruments can work on the principle of the pulse transit-time technique. In this case, electromagnetic pulses are transmitted towards the stored-material surface. The level measuring instrument then receives the signal components of this measurement signal that are reflected at the stored-material surface and at other reflectors if applicable, and generates therefrom an echo curve, which can be analysed to determine the level.
Level measuring instruments that work on the FMCW principle (FMCW: Frequency Modulated Continuous Wave) are also known. Again these can use guided signals or signals radiated into free space.
Particularly for users from the grain processing sector, but also for users from the gravel/concrete industry, there is an additional need for measuring instruments for continuous detection of the moisture (moisture content) of the material stored in the container or on the stockpile.
If the moisture content of the material stored in a container or on a stockpile (stored material) is intended to be measured, then a moisture meter is used for this purpose, as shown in FIG. 3 for example.
The moisture meter uses a direct time-measurement technique to determine the transit time of a measurement signal along a measuring probe located in the stored material. The relatively short time periods for which the measurement signal travels along the measuring probe through the stored material can result in inaccurate measurements. The measurement accuracy can be improved by averaging a plurality of measurements, although this greatly increases the power consumption of the moisture meter. This power consumption is then too high for a two-wire device.